If your tensioner fails, you hear bad noises. And typically you don't jump cam timing - the noise is bad enough that you at least keep the revs down until you get it fixed. Cam timing changes happened with the really really early 911s with a funky kind of chain rail with rubber parts on it - part of the rail would break off and get stuck between chain and gear, allowing a tooth to get skipped. And when that happens you should be getting air out the exhaust or the intake.

I assume you checked for intake and exhaust air leakage, right? Because you always can hear some leakage past the rings even with close to zero % leakdown figures. Think of a slow puncture leak in a tire - you can hear it, but the tire may take quite a while to lose much air. But if it sounds and feels like a gale, does sound like rings, and 40% is quite a lot (not as bad as, say, a holed piston, which should be 100%).